Method of manufacturing a heater



April 12, 1966 F. H. THALER 3,245,132

METHOD OF MANUFACTURING A HEATER Filed Dec. 50 1965 3 Sheets-Sheet 1 April 12, 1966 THALER 3,245,132

METHOD OF MANUFACTURING A HEATER Filed Dec. 50, 1965 S SheetS-Sheet 5 IN VENTOR. Hem z 6/ 715/115 United States Patent 3,245,132 METHQD OF MANUFACTURING A HEATER Frank H. Thaler, Belleville, N.J., assignor to Radio Corporation of America, a corporation of Delaware Filed Dec. 30, 1963, Ser. No. 334,376 8 Claims. (Cl. 2925.14)

This invention relates to electron discharge tubes, and particularly to a method of manufacturing coiled or helical heaters for use in electron discharge tubes.

In certain types of electron tubes having indirectly heated cathodes, it is desirable to heat the cathodes with a type of heater knw-on as a hairpin heater. Such heaters comprise an elongated helix of wire which is formed into a hairpin or V-shape. A reason such heaters are used is that the arrangement of the turns and legs of the heater causes cancellation of the electrostatic fields produced by the heater current. Such fields cause noise in the output of electron tubes, as is known.

In the manufacture of hairpin type heaters it is the practice to first wind at suitable wire, such as tungsten, on an elongated mandrel to form a plurality of connected heater workpieces. Thereafter, the wound mandrel is cut to provide individual workpieces, each workpiece comprising a length of mandrel having a helix of wire therear'ound. Each heater workpiece is then bent into V-shape, the ends of the legs of the V-shaped workpieces are secured to a clip, and the heaters then immersed in an insulating material bath for coating the heater workpieces with insulating material. Thereafter, the coated heater workpieces are immersed in an etchant that attacks and dissolves the mandrel but not the heater wire or insulation coating.

Heaters made by the above-described method are relatively costly. This is because after the wound mandrel is cut into separate workpieces, each workpiece is separately formed into V-shape, and each workpiece is individually mounted in the clip for immersion into the insulating bath. The individual handling of the heater workpieces is a tedious and time-consuming operation.

An object of this invention is to provide a new and improved method of fabricating electron tube heaters.

A further object of this invention is to provide a new and improved method of fabricating hairpin type heaters wherein the heaters are handled and operated on in bulk rather than individually.

For achieving these objects in accordance with a preferred embodiment of this invention, a method is provided wherein a wire is first wound onto an elongated mandrel to provide a strand. The strand, in turn, is then wound into a helix around a pair of spaced and parallel rods. One of the rods preferably has a larger diameter than the other, hence, the turns of the helix are wound with a generally triangular or wedge-shaped cross section. Each turn of the helix is fixed to the larger of the rods but not to the smaller. After winding, the smaller rod is removed leaving a workpiece consisting of a plurality of substantially V-shaped loops secured to and extending away from a common support r-od. Each loop is a heater workpiece.

Thereafter, the support rod is secured to a suitable clip, and the heater work-piece loops are immersed in an insulating material bath for coating the workpieces. The legs of the heater workpieces are then cut adjacent to the support rod, thereby providing V-sh-aped and coated wire wound mandrel workpieces. The mandrels are then dissolved from within the wire winding of each workpiece to complete the process.

In the drawings:

FIG. 1 shows an elongated mandrel having a heater wire wound therearound to provide a strand;

FIG. 2 illustrates the step of winding the strand shown in FIG. 1 around a pair of spaced support rods;

FIG. 3 is a view along line 33 of FIG. 2;

FIG. 4 illustrates the workpiece produced by the step illustrated in FIGS. 2 and 3;

FIG. 5 is a view along line 5-5 of FIG. 4;

FIG. 6 illustrates the step of stretching the support rod to which the workpiece loops are secured;

FIG. 7 illustrates the step of reverse bowing the support rod for straightening it;

FIG. 8 showsthe workpiece mounted in a clip suitable for use in the step of immersing the workpiece loops into an insulating material bath;

FIG. 9 illustrates the step of cutting the heater workpiece l-oops from the support rod; and,

FIG. 10 shows a finished hairpin type heater.

With reference to FIG. 10, a hairpin type heater comprises a helix 12 of wire 18 formed into V-shape and having a pair of legs 13 and 14, and an apex 15. The helix may be wound with a relatively fine pitch, and is coated with an insulating material such as aluminum oxide. Extending portions 16 and 17 of legs 13 and 14 are not coated in order to facilitate securing the heater to suitable supports (not shown) in electron tubes. The heater wire 18 is generally tungsten.

The method of fabricating such hairpin type heaters, according to one embodiment of the present invention, is as follows:

The heater wire is first wound onto an elongated mandrel 20 (FIG. 1). If the heater wire 18 is tungsten, a molybdenum mandrel is preferably used for reasons described hereinafter. Apparatus for winding the wire 18 onto the mandrel 20 is not shown since such apparatus is known. The mandrel 20 and the wire 18 wound therearound will hereinafter be referred to as the heater strand 22. For convenience, the heater strand may be wound onto a spool.

Thereafter, the heater strand is wound around a pair of spaced and parallel support rods 24 and 26, as shown in FIGS. 2 and 3. Rod 26 has a larger diameter than rod 24 for reasons described below. Only part of the apparatus used for winding the heater strand 22 onto rods 24 and 26 is shown since such apparatus is substantially the same as apparatus used for fabricating conventional grid electrodes for electron tubes.

As shown in FIG. 2, the rods 24 and 26 are secured to a tail-stock 28 which is mounted for axial movement to the left, as viewed in FIG. 2, and for rotation around the axis of movement. As the tail-stock 28 moves to the left it draws rods 24 and 26 from supply spools (not shown) mounted to the right of a winding head 30. The spools are mounted for rotation about the axis of rotation of the tail-stock 28 and in synchronization with the tailstock. The rods 24 and 26 are drawn through the winding head 30 and along grooves 32 and 34 (FIG. 3) along the sides of a mandrel 36. Mandrel 36 is mounted in winding head 30 and also rotates in synchronization with the tail-stock and about the same axis. A spool 38 of the heater strand is mounted adjacent to the winding head 30, and one end of the heater strand 22 is secured to rod 26. As the rods 24 and 26 are advanced and rotated by tail-stock 28, the heater strand 22 is wound in a helix around the two rods 24 and 26.

A pair of notching and peening rollers 42 and 44, respectively, are employed for notching rod 26 and peening closed the notches. During winding, a turn of the heater strand 22 is placed in each notch, and the notch then peened closed to lock the heater strand therein. Rod 24.

is neither notched nor peened. Notching and peening of only rod 26 may be accomplished by using a mandrel 36 having an off-center axis of rotation whereby rod 26,

sweeps out a cylinder of greater radius than the cylinder 3 swept out by rod 24. By proper positioning of rollers 42 and 44 only rod 26 is acted on by rollers 42 and 44.

The step of winding the heater strand 22 onto the spaced rods 24, 26 may be performed using substantially identical apparatus and techniques to those which are used in the manufacture of conventional grid electrodes. Differences exist, however, in that conventional grid electrodes normally employ rods of equal diameter, and in that the wire wound in a helix around the support rods of grid electrodes is normally notches and peened to both rods. The changes necessary to modify conventional grid making apparatus for performing the helix winding step of the present invention will be apparent to those skilled in the art and is not further described.

After the helix winding step described, the workpiece 50 thus produced is removed from the winding apparatus, and rod 24, which is not secured to the heater strand turns, is removed. The workpiece St is illustrated in FIGS. 4 and 5. Because of the differences in size of rods 24- and 26, the cross section of the strand turns or loops is substantially triangular or wedge-shaped. The size of rod 24 determines the radius of apex 15, and rods 24 and 26 determine the angle between the legs 13 and 14 of the turns.

For relieving the stresses producd in the support rod 26 and the heater strand 22 during the winding operation and for setting the shape of the wound turns, the workpiece 50 is annealed. This may be accomplished by firing the workpiece around 800 C. in a hydrogen atmosphere.

It frequently occurs that the back-bones or side rods of grids wound on grid lathes have a slight bow. Likewise, it may occur that rod 26 of workpiece 50 also has a slight bow, as illustrated (greatly exaggerated) in FIG. 4-. To facilitate further handling of the workpiece 50, as described hereinafter, the side rod 26 is straightened by a stretching operation as shown in FIG. 6. Each end of rod 26 is secured to a clamp 52 and the clamps moved apart. For a rod 26 having a length of six inches, and strand 22 wound at 30 turns or loops to the inch, the rod 26 may be stretched 0.1 inch. It is found that greater stretching tends to open the peened notches in rod 26. Further straightening of rod 26 may be achieved by mounting the workpiece 56 in a U-shaped support 54, as shown in FIG. 7. An adjustable block 56 is mounted midway between the ends of support 54, and rod 26 is given a slight reverse bow by means of a tool 58.

The heater strand loops are thereafter coated with an aluminum oxide insulating material. For accomplishing this, rod 26 is secured to a spring loaded clip 60 (FIG. 8) having a pair of jaws for snugly engaging rod 26. The inside of each jaw may be provided with a groove 62 to provide accurate positioning of the rod 26 with respect to the jaws 60. The use of a straight rod 26 simplifies mounting of the workpiece 50 into the clip.

The workpiece 50 is then lowered into an insulating material bath (not shown) to a preselected depth to coat portions of the strand loops. Portions of the loops closely adjacent to rod 26 are not coated to provide the uncoated leg lengths 16 and 17 (FIG. The insulating material may be cataphoretically coated onto the heater loops, hence, clip 66 is preferably made of an electrically conductive material and is provided with an electrical con ductor 64 for polarizing the strand loops with respect to the insulating material bath. After coating, the insulating coating may be protected by providing the workpiece loops with a second coating, such as Lucite. The second coating step may be performed by dipping the workpiece loops into a Lucite bath.

After the workpiece loops have been coated, the loops are cut from rod 26. The loops are cut through the uncoated portions 16 and 17. A suitable fixture 70 in which this may be accomplished is illustrated in FIG. 9. Fixture 70 comprises a base 72, a back-up member 74 against which rod 26 may be pressed for accurately posi- 4- tioning the workpiece 50, a spring loaded clip 76 for holding rod 26 in place, and an elongated cutter 78 for cutting the strand loops from rod 26.

The aluminum oxide insulating material, as well as the Lucite coating, if provided, is relatively stiff and brittle, hence, preserves the shape of the heater strands after they are cut from support rod 26. After cutting, the coated heater strands have a V-shape. Thereafter, the coated and shaped heater strands may be fired at around 1600 C. to set the heater wire 20 and to harden the insulation coating. The firing operation burns off the Lucite coating.

The heater workpieces are then etched in a suitable etchant which dissolves the mandrel 20 but not the wire 18 wound therearound nor the insulating coating. For heater strands comprising tungsten wire, molybdenum mandrel's, and aluminum oxide insulation coatings, a suitable etchant comprises a mixture of sulphuric and nitric acids. The finished heater is shown in FIG. 10.

Among the advantages of this method of manufacture are that the individual heater workpieces are formed, coated, and etched in bulk, no operations on individual heater workpieces being required. Accordingly, the cost of fabricating the heaters is considerably less than the cost of making heaters according to prior art methods.

Heaters having other shapes may be made by the method described. Thus, heaters having parallel legs may be provided by using rods 24 and 26 having equal diameters. Likewise, horseshoe-shaped heaters may be provided by securing the strand 22 to the small diameter rod 24 rather than to the large diameter rod 26. The resulting heater will have a large radius apex and inwardly converging legs.

In a specific example, a 1.7 mil tungsten wire 18 is first wound around a 5 mil molybdenum mandrel 20 at 200 turns per inch. The wound mandrel, or heater strand 22, is wound around a pair of rods 24 and 26 having 10 and 40 mil diameters, respectively, at 30 turns per inch. The strand loops are coated to a diameter of 15 mils, legs 13 and 14 are 15 mm. in length, uncoated portions 16 and 17 are 2 mm. in length, and the apex 15 of the heater has an outside radius of less than 40 mils.

What is claimed is:

1. A method of fabricating heaters for electron tubes comprising winding a wire on an elongated mandrel, winding the wound mandrel in a helix around a pair of spaced rods, securing the turns of said helix to one of said rods, removing the other of said rods from within said turns, and cutting said turns from said one rod.

2. A method of fabricating heaters for electron tubes comprising winding a wire on an elongated mandrel, winding the wound mandrel in a helix around a pair of spaced rods, securing the turns of said helix to one of said rods, removing the other of said rods from within said turns, setting the shape of said turns, and cutting said turns from said one red.

3. A method of fabricating heaters for electron tubes comprising winding a Wire on an elongated mandrel, winding the wound mandrel in a helix around a pair of spaced rods, securing the turns of said helix to one of said rods, removing the other of said rods from within said turns, coating portions of said turns with an insulating material, setting the shape of said turns, cutting said turns from said one rod, and removing said mandrel from within said wire winding of each of said out turns.

4. A method of fabricating heaters for electron tubes comprising winding a wire on an elongated mandrel, winding the wound mandrel in a helix around a pair of spaced rods, notching one of said rods and laying a turn of said helix in each of said notches during said winding, peening closed said notches for securing said turns to said one rod, removing the other of said rods from within said turns, coating portions of said turns with an insulating material, setting said coated turns, cutting said turns from said one rod, and removing said mandrel from within said wire winding of each of said cut turns.

5. A method of fabricating heaters for electron tubes comprising winding a wire on an elongated mandrel, winding the Wound mandrel in a helix around a pair of spaced rods, notching one only of said rods and laying a turn of said helix in each of said notches during said winding, peening closed said notches for securing said turns to said one rod, removing the other of said rods from within said turns, annealing said one rod and said helix wound therearound, straightening said one rod, coating portions of said turns with an insulating material, setting said coated turns, cutting said turns from said one rod, and etching said mandrel from within said wire winding of each of said out turns.

6. A method of fabricating heaters for electron tubes comprising winding a wire on an elongated mandrel, winding the wound mandrel in a'helix around a pair of spaced rods having difierent diameters, securing the turns of said helix to the rod having the larger diameter, removing the other of said rods from within said turns, setting the shape of said turns, and cutting said turns from said larger diameter rod.

7. A method of fabricating heaters for electron heaters comprising Winding a wire on an elongated mandrel, winding the Wound mandrel in a helix around a pair of parallel and spaced rods having different diameters, securing the turns of said helix to the rod having the larger diameter, removing the other of said rods from within said turns, coating portions of said turns with an insulating material, setting the shape of said turns, cutting said turns from said larger diameter rod, and etching the mandrel from within said wire winding of each of said out turns.

8. A method of fabricating heaters for electron tubes comprising winding a wire on an elongated mandrel, winding the wound mandrel in a helix around a pair of parallel and spaced rods having different diameters, notching the larger one of said rods and laying a turn of said helix in each of said notches during said winding, peening closed said notches for securing said turns to said larger rod, removing the other of said rods from within said turns, annealing said larger rod and said helix Wound therearound, straightening said larger rod, coating portions of said turns with an insulating material, firing said larger rod and said coated turns for setting said turns and for hardening said insulating material, cutting said turns from said larger rod, and etching said mandrel from within said wire winding'of each of said cut turns.

References Cited by the Examiner UNITED STATES PATENTS 331,663 1885 Thompson 2925.18 X 2,188,906 2/1940 Lackey 71.5 2,306,925 12/1942 Aicher 117-231 X FOREIGN PATENTS 628,236 9/1961 Canada.

603,341 1948 Great Britain.

JOHN F. CAMPBELL, Primary Examiner.

WHITMORE A. WILTZ, Examiner.

W. I. BROOKS, Assistant Examiner. 

3. A METHOD OF FABRICATING HEATERS FOR ELECTRON TUBES COMPRISING WINDING A WIRE ON AN ELONGATED MANDREL, WINDING THE WOUND MANDREL IN A HELIX AROUND A PAIR OF SPACED RODS, SECURING THE TURNS OF SAID HELIX TO ONE OF SAID RODS, REMOVING THE OTHER OF SAID RODS FROM WITHIN SAID TURNS, COATING PORTIONS OF SAID TURNS WITH AN INSULATING MATERIAL, SETTING THE SHAPE OF SAID TURNS, CUTTING SAID TURNS FROM SAID ONE ROD, AND REMOVING SAID MANDREL FROM WITHIN SAID WIRE WINDING OF EACH OF SAID CUT TURNS. 